sometimes i like to put seasonings, diced onions, jalapenos, barbecue sauce and worcestershire sauce in the beef before forming the burgers. other times ill go plain and just season wish salt and coarse ground pepper.

When you mix up the ground beef, try tossing in some onions, peppers, smoked cheddar, feta, basil, stuff like that. Just make sure you mince it so it won't make your patty fall apart on the grill. If you eat cheese on them, buy something you've never had before thats in the cheese kiosk like gouda, aged smoked cheddar, so on.

sautee some finely diced fresh mushrooms.
form a patty. take the back of a spoon and indent the middle of the patty. put a large spoonfull of the mushrooms into the indent. cover with ground beef work it back into patty shape. great way to get delicious mushrooms on your burger without them pricariously topped where they fall off. or mixed in where some bites dont have any mushroom.

I normally use 87-90% lean ground sirloin, mixed with quality garlic powder, salt, pepper, and sometimes either a little onion powder or LemonPepper/Montreal seasoning. However, even though I use quite a few spices, I use them fairly conservatively.